This invention generally relates to interferometry and more particularly to interferometric apparatus and methods by which highly precise metrology is practiced.
In highly precise metrology, it is required to understand and compensate for changes in the direction of propagation of various individual light beams in which information is encoded about distances or angles under measurement. Changes in the direction of propagation of such beams or in their angular relationships with respect to one another or some reference are often introduced by pitch, yaw, and roll of various optical components in the interferometer as, for example, those that might be experienced by a quickly slewing planar measurement mirror in a plane mirror interferometer, or the like. If such effects are not compensated, it is often not possible to achieve the desired precision required by important industrial applications such as those practiced in the fabrication of semiconductor devices.
In addition, where interferometers have dynamic elements that may be used to control the direction of propagating beams, some means for measuring errors in beam direction and a measurement of a change in an angle is needed to provide feedback signals for controlling such elements.
Consequently, it is a primary object of the present invention to provide apparatus and methods for simultaneous interferometric measurements of angular orientation of and distance to a plane mirror measurement object using a multiple beam interferometer system.
Other objects of the invention will in part appear hereinafter and will in part be obvious when reading the following detailed description in connection with the accompanying drawings.
Apparatus and method are described for simultaneous interferometric measurements of angular orientation of and distance to a plane mirror measurement object using a multiple beam interferometer system. A first and second groups of the multiple beam interferometer systems have beams that contact the measurement object two times and three times, respectively, for simultaneous measurement of one or more of changes in the distance to and changes of the angular orientation in one plane or in two orthogonal planes of the measurement object.